1. Field of the Invention
This invention relates to an automotive driving control system, and more particularly to an automotive driving control system for controlling the driving state of an automobile determined by engine speed, torque and the like to a desired state in response to depression of the accelerator pedal.
2. Description of the Prior Art
In FIG. 1a, curves E1, E2 and E3 are contour lines joining points of equal specific fuel consumption in an ordinary automobile depicted on an orthogonal coordinate system which is used to express the operating state of an automobile, the abscissa and the ordinate respectively representing the engine speed (Ne) and the engine torque (Te). In other words, in the ordinary automobile in which a transmission having set transmission ratios is used and the engine output and/or the vehicle speed are controlled by changing the opening degree of the throttle valve, it is necessary to set the engine so that the region D of minimum specific fuel consumption corresponds to an opening degree of the throttle valve slightly smaller than the full or maximum opening degree in order to obtain a large torque during, for instance, acceleration by full opening the throttle valve and at the same time actuating, for instance, an air-fuel ratio enriching device, thereby ensuring reserve torque. When controlling the driving state of an automobile provided with such an engine, it is preferred that the operating state of the automobile be caused to fall within the region D of minimum specific fuel consumption bounded by the curve E1 or near thereto. Curve A in FIG. 1a is a contour line, for the full-opening degree of the throttle valve.
In Japanese Unexamined Patent Publication No. 53(1978)-134162, there is disclosed a fuel consumption saving type automotive driving control system embodying a concept for improving the specific fuel consumption. In the control device, the opening degrees and the transmission ratios optimal for the purpose described above are calculated for various operating states of the automobile and mapped, and an optimal throttle valve opening degree and an optimal transmission ratio are read out from the map according to the particular amount of depression of the accelerator pedal to control the throttle valve opening degree and the transmission ratio of the transmission.
Further, it is known that any engine output which has conventionally been obtained with a fixed transmission ratio can be obtained with the throttle valve fixed at the full open position by changing the transmission ratio. In FIG. 1b, line A is an engine speed-torque characteristic curve showing the relationship between torque and speed in case that the throttle valve is fixed at the full open position (This curve will be referred to as "full open line", hereinbelow.), line B is the same in case that the transmission ratio is fixed (This curve will be referred to as "fixed gear line", hereinbelow.), and line C is the same in case that the engine output is fixed (This curve will be referred to as "fixed output line", hereinbelow.). In almost all the conventional automobiles, since a transmission having preset transmission ratios, e.g., first speed to fifth speed, is used and the engine speed-torque characteristics in the case of fixed transmission ratio are as shown by the fixed gear line B, it has been necessary to control the engine output by controlling the throttle valve opening degree. When it is assumed that the engine output is 80PS in a certain operating state on the fixed gear line B, e.g., operating state b corresponding to an engine speed of 3000 rpm and a torque T1, and when the engine speed is gradually lowered without changing the engine output, torque is increased along the fixed output line C as shown by the arrow c and takes value T2 at the intersection a of the fixed output line C and the full open line A, the value of the engine speed at the intersection a being 2000 rpm. This means that any engine output which has conventionally been obtained with a fixed transmission ratio can be obtained with the throttle valve fixed at the full open position by changing the transmission ratio. That is, by using a stepless transmission so that the transmission ratio can be continuously changed, the automobile can be controlled to a desired operating state with the throttle valve held full open. Further, since the engine output and the vehicle speed can be ensured, with this control system, by changing the transmission ratio, an engine having the region D of the minimum specific fuel consumption near the full open line A as shown in FIG. 1c can be used. Further in this control system, the pressure in the intake passage downstream of the throttle valve cannot become negative and accordingly pumping loss of the engine output can be substantially reduced.
In such a fuel consumption saving type automobile, it is preferred that the maximum acceleration performance be exhibited when the acceleration pedal is abruptly depressed by a large amount.